Watch for mail from the IRS or from the Department of the Treasury - Financial Management System. There should be an explanation in the mail from one of these sources that should explain why the refund was reduced.
Some common reasons for a partial refund include garnishments for child support, prior year taxes, or student loans that are in default. You can find out information about your refund by using the IRS's
Where's My Refund? tool. Or you can call the IRS at 1-800-829-1954 or 1-800-829-1040 to find out information about your refund.